Over 13% of the world's supply of edible oil in 1985 was produced from the oilseed crop species Brassica, commonly known as rapeseed or mustard. Brassica is the third most important source of edible oil, ranking behind only soybean and palm. Because Brassica is able to germinate and grow at relatively low temperatures, it is also one of the few commercially important edible oilseed crops which can be cultivated in cooler agricultural regions, as well as serving as a winter crop in more temperate zones. Moreover, vegetable oils in general, and rapeseed oil in particular, are gaining increasing consideration for use in industrial applications because they have the potential to provide performance comparable to that of synthetic or mineral/naphthenic-based oils with the very desirable advantage of also being biodegradable.
The performance characteristics, whether dietary or industrial, of a vegetable oil are substantially determined by its fatty acid profile, that is, by the species of fatty acids present in the oil and the relative and absolute amounts of each species. While several relationships between fatty acid profile and performance characteristics are known, many remain uncertain. Notwithstanding, the type and amount of unsaturation present in a vegetable oil have implications for both dietary and industrial applications.
Vegetable oils are subject to oxidative degradation, which can detract from the lubricity and viscosity characteristics of the oil as well as cause changes in color and odor perceived as undesirable. Color and odor are obviously of particular concern in food applications, where the autoxidation of vegetable oils, and the accompanying deterioration of flavor, is referred to as rancidity. The rate of oxidation is affected by several factors, including the presence of oxygen, exposure to light and heat, and the presence of native or added antioxidants and prooxidants in the oil. However, of most pertinence to the present invention, and perhaps generally, is the degree of unsaturation of the fatty acids in the oil.
The fatty acids present in vegetable oils are not equally vulnerable to oxidation. Rather, the susceptibility of individual fatty acids to oxidation is dependent on their degree of unsaturation. Thus, the rate of oxidation of linolenic acid, which possesses three carbon-carbon double bonds, is 25 times that of oleic acid, which has only one double bond, and 2 times that of linoleic acid, which has two. Linoleic and linolenic acids also have the most impact on flavor and odor because they readily form hydroperoxides.
Standard canola oil contains about 8-12% linolenic acid, which places it in a similar category as soybean oil with respect to oxidative, and hence flavor, stability. The oxidative stability of canola oil can be improved in a number of ways, such as by hydrogenating to reduce the amount of unsaturation, adding antioxidants, and blending the oil with an oil or oils having better oxidative stability. For example, blending canola oil with low linolenic acid oils, such as sunflower, reduces the level of 18:3 and thus improves the stability of the oil. However, these treatments necessarily increase the expense of the oil, and can have other complications; for example, hydrogenation tends to increase both the level of saturated fatty acids and the amount of trans unsaturation, both of which are undesirable in dietary applications.
High oleic oils are available, but, in addition to the possible added expense of such premium oils, vegetable oils from crops which have been bred for very high levels of oleic acid can prove unsatisfactory for industrial uses because they retain fairly high levels of polyunsaturated fatty acids, principally linoleic and/or linolenic. Such oils may still be quite usable for dietary applications, including use as cooking oils, but have inadequate oxidative stability under the more rigorous conditions found in industrial applications. Even the addition of antioxidants may not suffice to bring these oils up to the levels of oxidative stability needed for industrial applications; this is probably due to the levels of linolenic acid, with its extremely high susceptibility to oxidation, found in these oils.
As previously stated, oxidative stability is important for industrial applications to extend the life of the lubricant under conditions of heat and pressure and in the presence of chemical by-products. In such applications linolenic acid, and to a lesser extent linoleic acid, are again most responsible for poor oxidative stability.
Therefore, it would be desirable to obtain a variety of Brassica napus which is agronomically viable and produces seed oil having a level of oxidative stability sufficient to qualify it for use in dietary applications, and which would additionally be either sufficiently stable alone, or, depending on the precise application, sufficiently responsive to antioxidants, to find use in industrial applications.
European Patent Application EP 323753, to Allelix Inc., is directed to rapeseed oil having an oleic content of at least 79% and not more than 2% erucic acid. A table on page 10 discloses a fatty acid profile of what appears to be a preferred embodiment, constituting a selection designated Topas H6-90-99 with oil having an oleic acid content of 85.84%, a linoleic acid content of 3.54%, and an a-linolenic acid content of 2.68%.
International Application No. PCT/US91/01965, to Pioneer Hi-Bred International, is directed to rapeseed having a saturated fatty acid content of no more than 4% by weight in the form of stearic and palmitic acids, and a post-crushing and extraction erucic acid content of no more than about 2% by weight. As shown by Tables D, G, and H on pages 30, 38, and 39 respectively, the resulting oil also has an oleic acid content of no more than 70.64% by weight, a linoleic acid content of at least 14.24% by weight, and an .alpha.-linolenic acid content of at least 8.24% by weight.
International Application No. PCT/US91/05910, to E. I. du Pont, is directed to rapeseed seeds, plants, and oils having altered fatty acid profiles. Several such profiles are described, all of which contemplate a maximum erucic acid content of about 2%, combined with (a) FDA saturates of from about 4.2% to about 5.9% (page 3, lines 18-29), (b) oleic content of from about 69% to about 80% (page 3, line 30-page 4, line 11), (c) linoleic content of about 8.4% to about 14% (page 4, lines 12-23), (d) palmitic acid content of from about 2.7% to about 3.5% (page 4, lines 24-35), (e) palmitic acid content of from about 6% to about 12% (page 4, line 36-page 5, line 17), (f) stearic acid content of from about 0.8% to about 1.1% (page 5, lines 18-27; the reference to palmitic acid at page 5, line 26 would appear to be in error), and (g) linoleic plus linolenic acid content of no more than about 14%, preferably 12.5% (page 5, line 28-page 6, line 2).
International Application No. PCT/US92/08140, to E. I. du Pont, is directed to rapeseed having seed with reduced glucosinolates (and thus reduced sulfur), as well as reduced linolenic acid. The result was a rapeseed having an .alpha.-linolenic acid content of about 7% or less (see page 5, lines 5-10), more preferably less than or equal to about 4.1% (page 5, lines 19-23). The lowest content actually obtained appears to have been 1.9%, which was accompanied by relatively low levels of oleic acid (64.1%) and high levels of linoleic acid (25.7%).